Chlamydia trachomatis is an obligate intracellular gram-negative organism that is the leading cause of bacterial sexually transmitted infections worldwide. In the United States, the Center for Disease Control reported over 1.4 million cases of Chlamydia in 2013. See, Miller et al., JAMA, 291(18):2229-36 (2004); Ahmed et al., Morb. Mortal. Wkly. Rep., 58(14):362-5 (Apr. 17, 2009); Torrone et al., Morb. Mortal. Wkly. Rep., 63(38):834-38 (Sep. 26, 2014). The most common clinical manifestations of Chlamydia infections are urethritis and epididymitis in males, and cervicitis and pelvic inflammatory disease (PID) in females. PID potentially leads to serious chronic long-term sequelae including ectopic pregnancy and infertility. See, Westrom et al., J. Br. Fer. Soc.; 1(1):23-30 (1996); Dunne et al., Sex. Transm. Dis., 35(11 Suppl):S1-52 (November 2008); Schachter et al., Curr. Opin. Infect. Dis.; 15(5):491-5 (October 2002). In addition, Chlamydia infection increases the likelihood of human immunodeficiency virus (HIV) transmission and human papilloma virus (HPV)—induced neoplasia. See, Plummer et al., J Infect. Dis., 163(2):233-9 (February 1991). Treatment with antibiotics is not efficient in preventing recurring infections, and such treatment interferes with development of natural immunity. See, Brunham et al., J. Infect. Dis., 192(10):1836-44 (Nov. 15, 2005); Gotz et al., Scand. J. Infect. Dis., 34(1):28-34 (2002). Further, antibiotic therapy against Chlamydia does not necessarily eradicate chronic infection or affect established pathology. See, Ou et al., International Immunopharmacology, 16: 505-513 (2013).
The Chlamydia major outer membrane protein (MOMP) is a vaccine candidate protein containing both B- and T-cell epitopes and that induces protective, cross-reactive immunity in animal models of immunization and genital/respiratory challenge with different Chlamydia serovars. See, Pal et al., Infect. Immun., 73(12):8153-60, PMCID: PMC1307068 (December 2005); Pal et al., Vaccine 24(6):766-75 (Feb. 6, 2006); Kari et al., J Immunol., 182(12):8063-70, PMCID:PMC2692073 (Jun. 15, 2009); Li et al., Clin. Vaccine Immunol., 14(12):1537-44, PMCID:PMC2168373 (December 2007). MOMP is a trimeric porin with a 16-stranded β-barrel transmembrane core region with eight surface-exposed loops per each monomer, and containing four regions of sequence variability (variable domains or VDs) located within loops 2, 3, 5, and 6. See, Feher et al., PLoS ONE, 8(7): e68934, PMCID:PMC3723809 (2013); Sun et al., J Bacteriol., 189(17):6222-35, PMCID:PMC1951919 (September 2007); Rodriguez-Maranon et al., Protein Sci., 11(7):1854-61. PMCID:PMC2373662 (July 2002); Stephens et al., J. Bacteriol., 169:3879-85 (1987); Peterson et al., Infect. Immun., 59(11):4147-53, PMCID:PMC259009 (November 1991); Zhong et al., Infect. Immun., 58(5):1450, PMCID:PMC258646 (May 1990). The VDs are highly immunogenic and elicit cross-serovar neutralizing monoclonal and polyclonal antibodies and T cell responses in animal and human models. See, Baehr et al., Proc. Natl. Acad. Sci. U.S.A., 85(11):4000-4, PMCID:PMC280348 (June 1988); Ortiz et al., Infect. Immun., 68(3):1719-23, PMCID:PMC97337 (March 2000); Farris et al., Infect. Immun., 79(3):986-96, PMCID:PMC3067520 (March 2011); Pal et al., Infection and Immunity, 65(8): 3361-69 (1997). A single VD peptide as a vaccine has shown varying immunogenicity among mice of different haplotypes. See, Motin et al., Clinical and Diagnostic Laboratory Immunology, 6(3): 356-63 (1999).
Significant challenges in production and scale-up of this antigen exist for use of MOMP as a human Chlamydia vaccine. Purification of MOMP in native or recombinant form involve addition of detergents, has overall poor yields, and loses conformational epitopes during refolding. Scale up of an intracellular pathogen is not feasible for production. Vaccines using recombinant unfolded MOMP, MOMP peptides, or MOMP DNA-expressing plasmids have shown limited success. See, Pal et al., Vaccine, 24(6):766-75 (Feb. 6, 2006); Su et al., Vaccine, 13(11):1023-32 (August 1995); Pal et al., Vaccine, 15(5):575-82 (April 1997); Pal et al., Vaccine, 17(5):459-65 (Feb. 5, 1999); Shaw et al., Infect. Immun., 70(3):1097-105, PMCID:PMC127771 (March 2002); Tifrea et al., Vaccine, 29(28):4623-31, PMCID:PMC3114171 (Jun. 20, 2011); Tifrea et al., Infect. Immun., 81(5):1741-50, PMCID:PMC3648024 (May 2013); Schautteet et al., Vaccine, 29: 1399-1407 (2011). For example, MOMP peptides of a single variable domain have limited effectiveness among a variety of mice strains. See, Motin et al., Clinical and Diagnostic Laboratory Immunology, 6(3): 356-63 (May 1999).
Chlamydia trachomatis is the most common bacterial sexually transmitted infection worldwide with highest rates of infection, particularly in impoverished urban neighborhoods. See, Miller et al., JAMA, 291(18):2229-36 (May 4, 2004); Ahmed et al., Morb. Mortal. Wkly. Rep., 58(14):362-5 (Apr. 17, 2009); Torrone et al., Morb. Mortal. Wkly. Rep., 63(38):834-38 (Sep. 26, 2014). Clinical manifestations of Chlamydia differ in males and females, and the infection is often asymptomatic in women. Long-term sequelae such as chronic abdominal pain, ectopic pregnancy, and infertility are of concern. See, Westrom, J. Br. Fer. Soc., 1(1):23-30 (1996); Dunne et al., Sex. Transm. Dis., 35(11 Suppl):S1-S2 (November 2008); Schachter et al., N. Engl. J. Med., 298(8):428-35 (Feb. 23, 1978). Treatment with antibiotics does not prevent recurring infections, and reduces the off-set of high costs of medical treatments and interferes with development of natural immunity against the pathogen. See, Brunham et al., 0.1 Infect. Dis., 192(10):1836-44 (Nov. 15, 2005); Gotz et al., Scand. J. Infect. Dis., 34(1):28-34 (2002).
As multidrug resistant strains of Chlamydia have emerged to decrease effectiveness of antibiotic treatment, a reliable and effective Chlamydia vaccine is urgently needed. See, Ou et al., International Immunopharmacology, 16: 505-513 (2013).